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Li H.,China University of Technology | Song H.,Shanghai University | Liu W.,Shanghai University | Xia S.,Shanghai University | And 3 more authors.
Ultramicroscopy | Year: 2015

The segregation of various elements at grain boundaries, precipitate/matrix interfaces were analyzed using atom probe tomography in an austenitic precipitation strengthened stainless steel aged at 750. °C for different time. Segregation of P, B and C at all types of interfaces in all the specimens were observed. However, Si segregated at all types of interfaces only in the specimen aged for 16. h. Enrichment of Ti at grain boundaries was evident in the specimen aged for 16. h, while Ti did not segregate at other interfaces. Mo varied considerably among interface types, e.g. from segregated at grain boundaries in the specimens after all the aging time to never segregate at γ[U+02B9]/γ phase interfaces. Cr co-segregated with C at grain boundaries, although carbides still did not nucleate at grain boundaries yet. Despite segregation tendency variations in different interface types, the segregation tendency evolution variation of different elements depending aging time were analyzed among all types of interfaces. Based on the experimental results, the enrichment factors, Gibbs interface excess and segregation free energies of segregated elements were calculated and discussed. © 2015 Elsevier B.V.


Liu T.,Shanghai University | Xia S.,Shanghai University | Li H.,Shanghai University | Zhou B.,Shanghai University | And 3 more authors.
Journal of Materials Research | Year: 2013

Grain boundary engineering (GBE) has been carried out in nickel-based Alloy 690 with different initial grain sizes. The microstructure evolution during GBE-processing is characterized using electron backscatter diffraction to study the initial grain size effects on the grain boundary network (GBN). The microstructures of the partially recrystallized samples revealed that the GBE-processing is a strain-recrystallization process, during which each grain-cluster is formed by multiple twinning starting from a single recrystallization nucleus. Taking into consideration the coincidence site lattices (CSLs) and Σ, which is defined as the reciprocal density of coincidence sites, a high proportion of low-Σ CSL grain boundaries (GBs) and large grain-clusters are found to be the features of GBE-processed GBN. The initial grain size has a combined effect on the low-Σ CSL GBs proportion. A large initial grain size reduces the number of recrystallization nuclei that form, increasing the cluster size, but decreasing twin boundary density. On the other hand, smaller initial grain sizes increase the density of twin boundary after recrystallization, while decreasing grain-cluster size. Neither the grain-cluster size nor the twin boundary density is the sole factor influencing the proportion of low-Σ CSL GBs. The ratio of the grain cluster size over the grain size governs the proportion of low-Σ CSL GBs. © 2013 Materials Research Society.


Li H.,Shanghai University | Li H.,Jiuli Hi Technology Metals Co. | Song H.,Shanghai University | Liu W.,Shanghai University | And 4 more authors.
Ultramicroscopy | Year: 2015

The segregation of various elements at grain boundaries, precipitate/matrix interfaces were analyzed using atom probe tomography in an austenitic precipitation strengthened stainless steel aged at 750 °C for different time. Segregation of P, B and C at all types of interfaces in all the specimens were observed. However, Si segregated at all types of interfaces only in the specimen aged for 16 h. Enrichment of Ti at grain boundaries was evident in the specimen aged for 16 h, while Ti did not segregate at other interfaces. Mo varied considerably among interface types, e.g. from segregated at grain boundaries in the specimens after all the aging time to never segregate at γ'/γ phase interfaces. Cr co-segregated with C at grain boundaries, although carbides still did not nucleate at grain boundaries yet. Despite segregation tendency variations in different interface types, the segregation tendency evolution variation of different elements depending aging time were analyzed among all types of interfaces. Based on the experimental results, the enrichment factors, Gibbs interface excess and segregation free energies of segregated elements were calculated and discussed. © 2015 Elsevier B.V.

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